CA1121565A

CA1121565A - Process and apparatus for the manufacture of fibrous webs

Info

Publication number: CA1121565A
Application number: CA000335853A
Authority: CA
Inventors: KARL K. K. KRõYER
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-09-18
Filing date: 1979-09-18
Publication date: 1982-04-13
Also published as: ES492084A0; ZA794918B; NL7906936A; SE7907701L; ES8103228A1; FR2436209B1; FI792895A; DE2937531A1; DK144426C; DK144426B; BE878828A; JPS5590662A; GB2031970B; GB2031970A; NO792994L; AU5077779A; IT1123717B; LU81691A1; DK412778A; ES484211A1

Abstract

ABSTRACT:
In a process for the manufacture of fibrous webs comprising passing an endless air-permeable forming wire below a number of fibre distributors discharging fibres thereon so as to form a fibre layer, the forming wire used having openings of an area exceeding 1 m2 and the fibre material passing through the forming wire below a given fibre distributor being passed to one or more of the following fibre distributors.

Description

1~21565 mis invention relates to a process for the manufacture of fibrous webs, preferably webs of cellulose fibres, wherein an endless air-per~eable form-ing wire is passed below a number of fibre distributors, discharging fibres which under the influence of one or more suction boxes provided at the opposite side of the forming wire are sucked towards the forming wire so as ~o form a fibre layer thereon.
When manufacturing fibrous discharging webs by a prior art process of the above mentioned type, the fibre distributors are mounted at intervals along the endless air-permeable forming wire and a suction box is provided at each fibre distributor.
Copending Canadian application No. 315,945 filed November 7, 1978 dis-closes a process, wherein an endless air-permeable forming wire is passed belaw a fibre distributor consisting of a number of fibre distributor units which are built together and under which there is provided a suction box which is co~mon for these fibre distributor units and which serves to keep the fibrous layer con-stantly sucked against the wire while its thickness gradually increases.
The invention is based on the discovery that by using a process of the above mentioned type a fibrous product can be obtained having at least one sur-faoe layer which mainly consists of relatively long fibres and a central layer mainly consisting of relatively short fibres.
A fibrous product of such a composition is especially soft and has a gcod feed. Therefore, it is suitable for the manufacture of relatively light fibrous products, especially fibrous products having a weight of less than 100 g/m . Such products æe p æ ticulaxly suitable for use as tissue paper including facial tissue, paper towels, toilet paper etc.
The process of the invention is characterized in that the air-permeable endless wire has op~nings having an area ex oeeding 1 mm and that the fibre mate-rial passing through the wire below a given fibre distributor is passed to one or --1-- .~",0`~

l~Z1565 more subsequent fibre distributors viewed in the direction of movement of said wire.
By using a wire having cpenings with an area of above 1 mm2 only relatively long cellulosic fibres discharged from the first of the number of fibre distributors are retained by the wire, whereas the relatively short fibres will pass through the wire and down into the suction box.
The relatively long fibres of the fibrous material passing through the forning wire under the first fibre distributor are deposited there--la-'~ :

~2~5 on, whereas the shor-t fibres again will pass through the wire when said fibres are recycled to the Following fibre distributor and then are sucked towards the forming wire with the long fibres already deposited thereon. As the fibre layer becomes thicker, it also becomes 5 more dense and even relatively short Fibres will gradually be deposited thereon .
When preparing fibrous products in the form of webs by using several fibre dis-tribu-tors each consisting of a number, for example 6, fibre distributor units and by supplying fresh fibrous material to 10 each fibre distributor, a fibrous product in which both surface layers predominantly consis-ts of relatively long -fibres can be obtained.
This is achieved by supplying fibre material consisting of rela-tively short fibres from the preceding fibre distributor to the rear portion of the last fibre distributor viewed in the direction of move-15 ment of the forming wire. In that case the relatively short fibres passrelatively quickly through the bottom of the fibre distributor and are deposited on the layer already formed on the forming wire. The relatively long -fibres, however, will be distributed over the whole fibre distributor including its front portion. Within the front portion 20 they will be subjected to strong influences frorn the stirring means provided therein because the relatively short fibres already have been discharged from the fibre dis-tributor. Under these circumstances the likelihood that these fibres will be brought into such a position rela-tively to the openings of the bottom of -the fibre distributor so that 25 they can pass through said bottom, is increased.
Consequently, a surface layer of relatively long fibres is formed - on top of the fibre layer already formed.
It should be mentioned that the term "distributor" herein is to be understood as comprising also one of the distributor units forming 30 part of a fibre distributor composed of several of such distributor units. In that case the fibre ma-terial which has passed the forming surface below such a fibre distribulor unit is -transported to one or more of the following fibre distributor units which, For example, may be provided within the same housing.
A further advantage of -the process described is -that the fibre layer initially deposited on the -Forming surface acts as a filter for the mixture of fibres and air subsequently supplied thereto and conse-quently reduces the loss of fibre material. The result is that the production economy is improved and that the contamination problems lS65 are reduced to a minimum.
When manufacturing fibrous proclucts mainly consisting of cellu-losic fibres which ordinarily have a length of 0,5-3 mm, the forming wire used is preferably a wire having openings which in the cross machine direction have dimensions of from 0,5 to 1,5 mm. These open-ings are preferably elongated in the machine direction and the length of the openings in this direction are for example up to 3 times the width of the openings.
The forming wire preferably consists of a woven metal net in 10 which the warp and weft threads form a plain weave. It is preferable to use a net in which the distance between the weft threads is great-er than the distance between the warp threads so as to facilitate the cleaning of said net.
A particularly sui-table metal net is a net in which the metal 15 threads form a plain weave and in which the weft threads are straight, whereas the warp threads form bends at the crossing points. In such a net the weft threads are surrounded by the warp threads and con-sequently the risk that fibres accumulate a-t the crossing points is less than in the commonly used me-tal nets.
As mentioned above the forming wire preferably is a metal net.
However, it can also be prepared from threads of a plas-tics material and is not necessarily in the form of a woven product. Thus, the wire may be formed of a perforated metal or plastics film.
In a preferred embodiment of the process o-f the invention seve-25 ral, for example 3, fibre distributors are mounted along the forming wire, said fibre distributors each consisting of several, for example 6, fibre distributor units, each comprising a row of stirrers, said row extending transversely o-F the forming wire, the fibre material passing through the forming wire below the first fibre distributor being 30 transported to both the second and the third fibre distributor seen in the direc-tion of movement o-F said wire. In this manner a suitable air balance in the system of fibre distributors is obtained.
The transport of fibre material from the suction box below the first distributor to -the second and third fibre distributor is generated 35 partly by means of a fan mounted in a conduit connecting the suction box below the first distributor with the second and third fibre distri-butors and partly with an exhaustion device which is connected to the suction boxes below the second and third fibre distributors.
As mentioned above the fibre material from the suction box below `1 -~he l; sl fibre c.,s~ rir)uto~ is pref rably hlLroducecl in the real portio of the ~hird fibre distribu~ol which is also fed with fresh fibre mate-rial so as to obtain a top layer mainly consisting of long fibres.
~hen manufacturing relatively thin Fibrous webs by a process of -the type defined in the introductory part of the specification, one or more auxillary wires are ordinarily used for transporting the fibrous web removed from the forming wire to a drying s-tation.
By using the above mentioned relatively open -forming wire, it has been found that it is possible to introduce the thin Fibrous web formed on the forming wire direcl ly onto a drying cylinder. This dis-covery has significantly contributed to making an apparatus -For the manufacture of fibrous webs more compact and to reducing the build-ing, initial and operational costs for such an apparatus.
When the forming wire during the transfer oF the Fibrous web on-to the drying cylinder is pressed against said cylinder, e.g. by means of one or more pressure rollers, a surface pa~tern correspona-ing to the surface pattern of the wire is formed on both sides of the fibrous web. Consequently, the fibrous web is in contact witl~ the drying cylinder essentially only in a pattern of points or lines and corresponding -to the surface pattern of the forming wire.
This is of great importance as far as the subsequent removal of the dried fibrous web from the drying cylinder is concerned. Thus, previously a thin fibrous web ~,vhich adhering to a drying cylinder over the full contact area can be removed there-From only in connec-tion with the creping of said fibrous materiai. However, by utilizing the process of the invention, the -Fibrous web can be removed from the drying cylinder without simultaneously creping said fibrous web.
The fibres of the final fibrous web are bonded together by a binder. Such a binder may be supplied to the fibrous ma-terial in different ways. Thus, a solid binder, For example modiFied s-tarch which is activated by supplying moisture thereto, can be introduced into the deFibrator, For example a hammer mill, which is ordinarily used for preparing the defibra-ted ma-terial supplied to the fibre distributor .
When the binder is supplied to the Fibre distribu-tors together with -the defibrated material, a significant portion thereof will pass through the forming surface below the first fibre distributor and is therefore primarily deposited in the fibre layer provided on top of the first layer.

56~

In order to activate the binder, moisture, -For example water, is sprayed onto the fibre web while it is present on the forming wire.
Excessive amounts of water are removed during the contact between the fibrous web and the drying cylinder. During -the heating of the 5fibrous web the binder may be cured.
A binder in the form of a binder solution or suspension may also be sprayed onto the fibrous web while it is present on the forming wi re .
By using a thermocuring binder it may be necessary to heat the 10fibrous web to a higher temperature than the tempera-ture obtained during the contact between the fibrous web and the drying cylinder.
This can be achieved by passing -the fibrous web through a curing oven in which hot air is passed through the fibrous web after it has been removed from the drying cylinder.
15During such heat treatment with the object of curing the thermo-curing binder it is desirable to keep the fibrous web supported.
I n a preferred embodiment of -the process of -the invention such support is provided by using the return run of the forming wire as a support for the fibrous web during the curing process.
20Binder may also be supplied by applying to the surface of the forming wire, e.g. by rollers, a binder solution or suspension having a relatively high viscosity. The binder will primarily be deposited on the protruding zones of the wire (the crossing points in a woven metal net~ and will consequently be pressed into the fibrous web 25during the embossing which is effected when the -forming wire with the fibrous web located thereon is pressed against the drying cylin-der .
In this embodiment of the process oF the invention the binder will predominantly be located in the embossed points or lines and the 30intervening zones are not compressed correspondingly. Therefore, a product having a soft and absorbing surface and being voluminous is obtai ned .
The removal o-F -the fibrous web from the drying cylinder is pre-ferably effected with a doctor's knife. Depending on the shape and 35the mounting of such a knife, the fibrous web is removed in a creped or non-creped state. When the fibrous web is creped, the length thereof will ordinarily be reduced with about 20g6. In view of the manner in which the fibrous web is in contact with the surface of the drying cylinder, the fibrous web can be removed from said surface - '., , ~, ~L~2~565 without creping said web. Thus, a fibrous web having a smooth surface and essentially the same surface properties in all directions is obtai ned .
The invention also relates to an apparatus for the manufacture of 5 fibrous webs made from cellulosic fibres, said apparatus comprising an endless air-permeable forming wire, a number of fibre distributors mounted along said forming wire, one or more suction boxes co-operat-ing with each fibre distributor and mounted on the opposite side of said forming wire.
The apparatus according to the invention is characterized in that the forming wire has openings with an area exceeding 1 mm2 and that it comprises conduits connecting the suction box or suction boxes below a given fibre distributor with one or more subsequent fibre distributors viewed in the direction of movement of the -forming wire.
The distributors of the apparatus according to the invention are preferab!y of the type which comprises one or more rows of stirrers rotating in one or more planes which are essentially parallel to the surface of the -forming wire.
It is par-ticularly advantageous to use distributors of the t pe 2t~ disclosed in the specification of ~ patent applica-tion No. ~.6f~.
The individual fibre distributor uni1:s of such a fibre distributor are preferably provided within the same housing and the stirring zones are separated by separating walls of a type which allows fibre material from passing from one stirring zone to the adjacent one.
In an apparatus comprising three of these fibre distributors, each composed o-F for example 6 fibre distributor units, the suction box or suction boxes below the first fibre distributor is (are) pre-ferably connected with inlets of the second fibre distributor, said inlets opening in the middle portion of the fibre distributor housing and with inle-ts of the third fibre distributor opening in the rear portion of -the fibre distributor housing.
The suction box or suction boxes below the fibre distributors preferably comprise rollers suppor-ting the forming wire which is pas-sed above said suction box or suction boxes. Such supporting rollers are preferably mounted directly below the shafts of said stirring-means because it has been -Found that an optimum air distribution within the suction box or suction boxes is obtained with such a moun ting .
A spray cabin having means for spraying water or binder solu-7 ~2~5~;5 tion onto the fibrous web may be provided adjacent to the last fibre distributor in the row of such fibre distributors.
The transfer of the -Fibrous web onto the drying cylinder is preferably effected by pressing the fibrous web against said cylinder while it is still in contact with the forming wire.
Thus, the apparatus may comprise one or more rollers which both serve as supporting rollers for the -Forming wire and as pressure rollers pressing the forming wire and the fibrous web located thereon against the drying cylinder.
The pressure required may be generated by using a forming wire which encircles a substantiai portion, for example up to 180, of the periphery of the drying cylinder.
This embodiment is particularly preferable in case the return run of the forming wire extends above the row of fibre distributors and when it is desired to have that portion of the forming wire on which the fibrous web is to be formed at the floor level.
The drying cylinder used is preferably an internally heated drum. The surface of the drying cylinder is preferably heated to a temperature of 100-200C and in particular 120-160C.
The apparatus also comprises means for removing the fibrous web from the drying cylinder. It is preferable to use a doctor's knife having an edge which is pressed against the surface of the drying cylinder. As mentioned above, the means for removing the fibrous web from the drying cylinder may be constructed in a manner so as to simultaneously crepe the fibrous web. As is also mentioned above, the invention permits the removal of the fibrous web without effecting a creping.
The apparatus may also comprise one or more devices for winding up the fibrous web so as to form a roll. If the binder used is a thermocuring binder, the apparatus also comprises means for further heating the fibrous web before it is cooled and wound up.
The means for further heating the fibrous web preferably compri-se a suction box mounted on one side of an endless support belt and heatincl elements with air supply means mounted a-t the opposite side of said support belt.
When the fibrous web is to be subjected to such a further heat-ing, it is introduced on said support belt and it is sucked onto said belt under the influence of the vacuum in -the suction box. When the fibrous web is advanced together with the support belt, it is heated 8 3L~ 6S
by hot air which is generated by the heating elements and which under the influence on the vacuum in the suction box passes through the fibrous web.
In a particularly simple embodiment of the apparatus o-f the in-5vention, said support bel-t is a portion of the return run of the formi ng wi re .
The invention wiil now be described in further detail with re-ference to the drawings in which Fig. 1 shows a portion of a preferred metal net for use in 10the process of the invention, Fig. 2 shows the net illustrated in Fig. 1 in perspective, Fig. 3 shows a preferred embodiment of the apparatus accord-ing to the invention, and Fig. 4 shows another embodiment of the apparatus according 15to the invention.
The metal net illustrated in Figs. 1 and 2 consists of warp threads 1 and weft threads 2, the distance between the weft threads being greater than the distance between the warp threads. Therefore, the openings 3 in the net are rectangularly shaped. The warp threads 201 and the weft threads 2 form a socalled plain weave. However, the weft threads 2 are straight, whereas the warp threads 1 form bends at the crossing points with the wef-t threads. The net illustrated presen-ts the advantage that it is easy to remove fibres, fibre lumps, binder etc. therefrom when a brush rotating about an axis parallel to 25the longitudinal direction of the weft threads sweep over -the net because the weft threads are not adjacent to the surfaces of the net.
The apparatuses illustrated in Figs. 3 and 4 are in principle identical as far as the forming sections and the binder supply sec-tions are concerned and the same components in these sections of the 30apparatus therefore have the same reference numerals.
The forming section consists of three fibre distributors 10, 11 and 12 which are mounted successively over a forming wire 13 which is advanced in a direction illustrated by an arrow 14. Each fibre distributor consists of six fibre distributor units mounted in a common 35housing 15. Each fibre distributor unit comprises a number of stirrers mounted in a row perpendicular to the direction of movement of the forming wire 13. The stirrers 16 have impellers which are located a short distance above the bottom of the housing, said bottom having the form of a screen. Separa~ing walls 17 are provided between ad-jacent rows of stirrers 16. These separating walls 17 do not extend fully to the bottom of the housing 15 and consequently fibres may move from a zone below one row of stirrers 16 to the adjacent zone below another row of stirrers 16.
Below each fibre distributor 10, 11 and 12 there is provided a suction box 18, 19 and 20, respectively, containing several rollers 21 supporting the forming wire 13. The fibre distributors 10, 11 and 12 are connected with supply pipes 22,23 and 24, respectively, for freshly defibrated fibre material. The suction box 18 is connected with the middle portion of -the fibre distributor 11 and the rear por-tion of the fibre distributor 12 via a pipe 25 comprising an air pump 26. The supply pipes for freshly defibrated fibre material also open into the rear portion of the fibre distributor 12.
The suction box 19 is connected with an exhaust pump 29 via a connecting pipe 27 and the suction box 20 is connected with the ex-haust pump 29 via a connecting pipe 28. The apparatus shown also comprises a spraying cabin 30 mounted adjacent to the Fibre distribu-tor 12 and above the forming wire 13.
In the apparatus illustrated in Fig. 3 the return run of the forming wire 13 is located below the fibre distributors 10, 11 and 12 and the spraying cabin 30 and the forming wire is supported by rol-lers 31-36 of which the roller 34 is a guide roller and the roller 35 is a tension roller.
The apparatus illustrated in Fig. 3 further comprises a rotatable drying cylinder 37, a doctor's knife 38 and rollers 39, 40, 41 and 42 for supporting a fibrous web 43 formed in the apparatus before it is wound up so as to form a roll 44.
In the apparatus illustrated in Fig. 4 the forming wire 13 ex-tends around a drying cylinder 45 and the return run is supported by the rollers 46-50 of which the roller 47 is a guide roller.
The apparaLus illustrated in Fig. 4 also comprises a doctor's knife 51 and rollers 52, 53 and 54 for a fibrous web 55 which, when wound up, forms a r-oll 56.
A suction box containing some support rollers 58 for the forming wire 13 is mounted above the forming wire 13 between the drying cy-linder 45 and the roller 52. On the opposite side of the forming wire 13 there is mounted a drying oven 59 and conduits (not shown) for alr.

~21565 l~) ~ ;~)ell supl~ ying t, esl-lly d~ Fibrated cellulosic Fibrous md-ter,al optionciln,~ containing a minor arnollnt of synthetic Fibres, For example thermoplastic plastic fibres, to ~he -Fibre distributors 10-12 and by dischat-ging air with the exhaust p ump 29 and transporting air contain-~' ing relativeiy short fibres frorn the suc-tion box 18 to -the fibre di-stributors 11 and 12, a fibrous la~.,er is gradually Formed on the form-ing wire 13 of the appara-tus illustrated in Figs. 3 and 4, the bottom and top layers oF said fibrous layer predominan-tly consisting of rela-tively long -Fibres.
When the Fibrous layer has attained a desired thickness in the fibre distributor 12, it passes through the spraying cabin in which a binder solution can be applied to the fibrous layer.
In the apparatus illustrated in Fig. 3 -the fibrous layer is con-tacted with the drying cylinder 37 which e. g . is heated to a tempera-ture of 160C and at the same time i-t is strongly compressed.
The fibrous layer is then removed from the Forming wire 13 and during the rota-tion of the drying cylinder 37 it is contacted with the doctor's knife 38. At this stage the binder is cured and a seifgsup-porting fibrous web 43 is obtained. The web 43 is then wound up to form a roll 44.
A brush (not shown) is mounted along the re-turn run oF the forming wire 13 and between the rollers 32 and 36 in order to remove remaining fibres or binder From the forming wire 13.
The fibrous layer prepared by the apparatus illustrated in Fig.
4 is contacted with -the drying cylinder 45 while it is compressed be-tween said cylinder and the forming wire 13. During this contact a su-Fficient curing is initiated even when using a thermocuring binder to provide a fibrous web which, when it has been removed from the drying cylinder by means of the doc-tor's knife 51, is self-supporting.
After being removed from the drying cylinder the fibrous web 55 is brought into contact with the forming wire 13 under -the influence of the vacuum within -the suc-tion box 57.
During i-ts passage above the suction box 57 hot air generated in the drying oven 59 passes through the -fibrous web so as to complete-Iy cure the binder. The fibrous web 55 thus formed can subsequentlybe wound up in the form of a roli 56.
The return run of the forming wire 13 is cleaned in the same manner as discussed in connection wi-th Fig. 3.
I he invention will now be illustrated further with reference to ~Z1565 the fo owing e~<alnples:

~ MPLE 1 Cellulose pulp ~,type "Korsrlass Marma") and oxidized starch 5' ~ (type "Viscosol 220"~ in a proportion of 95% cellulose pulp and 5%
oxidized starch were introduced into a hammer mill. AFter forming a fibrous web in an apparatus as illustrated in Fig. 3 and compl ising a metal net having mesh openings ~ th an area of 1,5 mr~2, water con-taining 1?~ dissolved oxidized starch (type "Viscosol 220") was sprayed lO onto ~he fibrous web. Measurements showed that when fresh deFibrat-ed material is supplied to the three fibre distributors in equal a-mounts, about 20% of the -total amount of starting material passed -through the metal net below the l~irst fibre distributor and are trans-ferred to the second and third t ibre distribu-tor. Af-ter transferring 15 the fibrous layer from the metal net to the drying cylinder haviny a temperature of 120C, a product was obtained which, before it was removed from the drying cylinder with a creping knife, contained about 25% water. The product, the length of which had been reduced by about 25%, was wound up to form a roll. The fibrous product 20 obtained weighed 30 g/m2 and was suitable for -the manufacture of toilet paper and tissue paper.

A fibrous product was prepared from the same starting materials and by using the same technique as described in Example 1 with the exception that the temperature of the drying cylinder was 150 C and that the final product was wound up wi-thou-t any reduction of its leng-th. Due -to the use of -the increased temperature of the surface of the cylinder, the fibrous layer could be removed from -the ~rying cy-linder wi-thout creping the product. ThereFore, the fibrous product ob-tained could be wound up with a speed corresponding to -the rate at which it was -formed on -the forming wire.

A fibrous product was prepared in the same manner as described in Example 1, except -that -the arnount of cellulose pulp was 93% and that also 2% thermocuring melamin binder ~of the type "Cymell 411") were used. The product ob~ained weighed 25 g/m2. In order to obtain i2 a su~ iently nl~Jh wet strel-,clth the fibrous procuc-L rerrloved from the h~ r)g cyllnder- was heated to a temperaLure of 160 C ror 1-2 secon~ s ~

EXAMPLES_4-6 Fibrous product:s having difterent weigh-ts were prepared by the methods described in Examples 1-3. Thus, a fibrous product having a weight cf 75 g/m2 (Example 4) was prepared by the method according to Example 1, a fibrous prociuct havincJ a weight of 75 g/m2 ( Example 5) was prepared by the method according to Exai-nple 2 and a fibrous product having d weigh-t o-F 80 g~m2 ( Example 6) was prepared by the method according to Exarnple 3. The products having weights of 75 g/m2 and 80 g/m2 were sui-table for the manu-Facture of kitchen rolls and paper towels. The product con-taining the melamin binder had an 15 increased wet strength.

The method according to Example ~was repeated but by using a 20 melamin binder of the type "Cymell 430". Preliminary investigations o-f the product obtained showed no significant differences compared -to the product prepared according to Example 3.

A fibrous product was prepared as described in Example 1 bu-t with the excep-tion that part of -the cellulose pulp was replaced by thermoplastic polye-thylene in fibre form. The polyethylene fibres had essentially the same leng-th as the cellulosic fibres of the pulp materi-al. The material in-troduced onto the Forming wire had the Following 30 composition: 80% cellulosic -fibres, 15% polyethylene -Fibres and 5% oxid-ized starch. After the -Formation of the fibrous layer, a solution oF
oxidized s-tarch in water was sprayed thereon.
The product formed was more yeliow than -the product ob-tained according to Example 1 bu-t the quality o-f -the product was such that 35 it was suitable for use for -the manufac-ture oF toilet paper.

A product was prepared by -the method according to Example 1 6 ~ ~

~Z~L56S
i3 witll he excep~,oll that cl 15'-~, starcll solution was applie, -to L le formir j ~vire b~y roller~ belore tl,e fibrous layer was formecl thereon.
The product obLained was stronger bu-t no-t as soft as the product accorcing to Exar,lple 1.

_AMPLE 10 A fibrous product was prepared by the method described in Example 9 with -the exception that the concentra-tion of the solution contain ng oxidized s-tarch which was sprayed onto the fibrous layer before the latter was contacted wi-th the drying cylinder, only was

2%. The product ob-tained was suitable for the manufacture o-F ki-tchen rolls and the weight of the product was 60 g/m .

When products are prepared by the methods described in the above examples 1-10, the thickness o-F the material depends on the pressure under which the -Fibrous layer is pressed against the drying cylinder with the metal net and on -the temperature of the cylinder.
As a rule, however, produc-ts having a weight Of 30 g/m2 generally have a thickness of 0,3-0,4 mm, and products having a weight of 75 g/m2 have a thickness o-F about 0,8-0,9 mm.
All the products prepared according to the above examples showed a clear embossed pattern corresponding to tha-t of the metal net. The fibres were strongly bonded together within -the embossed zones and the product obtained had a considerable strength and were 25 voluminous, thus making such products suitable for the manufacture of toile-t paper and paper tissue.

Claims

C L A I M S

1. A process for the manufacture of fibrous webs, wherein an endless air-permeable forming wire is passed below a number of fibre distributors discharging fibres which under the influence of one or more suction boxes mounted at the opposite side of the forming wire are sucked towards the forming wire so as to form a fibre layer thereon, c h a r a c t e r i z e d in that the air-permeable endless forming wire has openings having an area exceeding 1 mm2 and that fibre material passing through the forming wire below a given fibre distributor is passed to one or more subsequent fibre distributors viewed in the direction of movement of the forming wire.

2. A process according to claim 1, c h a r a c t e r i z e d in using several fibre distributors, each consisting of a number of fibre distributor units and in supplying fresh fibre product to each of said fibre distributors.

3. A process according to claim 1 for the manufacture of cellu-losic fibre products, c h a r a c t e r i z e d in that the openings of the forming wire have a dimension in the cross machine direction of from 0,5 to 1,5 mm.

4. A process according to claim 3, c h a r a c t e r i z e d in that the dimension of the openings in the machine direction is 2-3 times the dimension of said openings in the cross machine direction.

5. A process according to claim 1, c h a r a c t e r i z e d in using a woven metal net in which the warp and weft threads form a plain weave.

6. A process according to claim 5, c h a r a c t e r i z e d in that the distance between the weft threads is higher than the distance between the warp threads.

7. A process according to claim 6, c h a r a c t e r i z e d in that the weft threads are straight and the warp threads form bends at the crossing points.

8. A process according to claim 1, c h a r a c t e r i z e d in that the fibrous web formed on the forming wire is directly introduced onto a drying cylinder.

9. A process according to claim 8, c h a r a c t e r i z e d in that the forming wire is pressed against the drying cylinder during the transfer of the fibrous web onto said drying cylinder.

10. A process according to claim 9, c h a r a c t e r i z e d in that a binder is applied to the forming wire before the formation of the ??rous layer thereon.

A process according to claim 8, c h a r a c t e r i z e d in that the drying cylinder is headed to a temperature of 100-200°C.

12. A process according to claim 8, c h a r a c t e r i z e d in that the fibrous web is removed From the drying cylinder without re-duction of length.

13. A process according to claim 12, c h a r a c t e r i z e d in that the fibrous web is further heated after being removed from the drying cylinder.

14. A process according to claim 13, c h a r a c t e r i z e d in that the fibrous web is supported by the return run of the forming wire during said further heating.

15. An apparatus for manufacturing cellulosic fibre webs compris-ing an endless air-permeable forming wire, a number of fibre distribu-tors mounted along said forming wire, one or more suction boxes co-operating with each of said fibre distributors and mounted at the opposite side of the forming wire, c h a r a c t e r i z e d in that the forming wire has openings having an area exceeding 1 mm2 and that it comprises conduits connecting the suction box or suction boxes below 3 given fibre distributor with one or more following fibre distri-butors viewed in the direction of movement of the forming wire.

16. An apparatus according to claim 15, c h a r a c t e r i z -e d in that it comprises means for supplying fresh fibre material to each fibre distributor and that the suction box of a given fibre distributor is connected with the rear end of the last fibre distributor in the series of fibre distributors, each consisting of a number of fibre distributor units built together.

17. An apparatus according to claim 15, c h a r a c t e r i z -e d in that it further comprises a drying cylinder mounted in direct connection with the forming wire.

18. An apparatus according to claim 17, c h a r a c t e r i z -e d in that it comprises one or more rollers which, apart from serving as support rollers for the forming wire serve as pressure rollers pres-sing the forming wire and the fibrous web located thereon against a drying cylinder.

19. An apparatus according to claim 17, c h a r a c t e r i z -e d in that the forming wire is mounted so as to encircle a significant portion of the drying cylinder.

20. An apparatus according to claim 19, c h a r a c t e r i z -in that the return run of the forming wire passes above the fibre distributors.

21. An apparatus according to claim 17, c h a r a c t e r i z -e d in that it has means for further heating the fibrous web after its removal from the drying cylinder.